The present invention relates to a metal surface treating agent and more specifically to a metal surface treating agent for aluminum or aluminum alloy in which adhesion with a coating and corrosion resistance are enhanced.
A cover material of aluminum alloy of a metallic can such as a beverage can and a food can is generally formed by degreasing a metal plate, applying a top coating onto the plate treated for the groundwork, and curing under heating. Here, treatments for the groundwork mean a surface treatment of a metal plate to be done for providing mainly adhesion with the top coating and corrosion resistance to the metal plate.
Though a chromate-phosphate surface treating agent has been used for the surface treatment of the cover material of aluminum alloy of the metallic can, the metal surface treating agent, which is a non-chromium surface treating agent that does not use chromium compound and can provide high adhesion with the top coating and corrosion resistance, is required in recent years on a request from environmental protection and market needs.
As a non-chromium chemical conversion treating agent, there is disclosed a surface treating agent for aluminum which contains zirconium and/or titanium, phosphate and fluoride in Japanese Kokoku Publication Sho-56-33468. However, this technology was insufficient as a coating ground of the cover material of aluminum alloy of the metallic can, in the high adhesion with the coating and the corrosion resistance as a coating material.
In Japanese Kokoku Publication Sho-63-30218, there is disclosed a non-chromium surface treating agent which is composed of water-soluble titanium and/or zirconium compounds, and tannic material and/or water-soluble or water-dispersant organic high polymer material. This technology is a combination of the above-mentioned inorganic compounds, the tannic material, a polymer or a copolymer of acrylic acids and esters thereof and a polymer or a copolymer of methacrylic acids and esters thereof selected as the organic high polymer material, and was insufficient in the corrosion resistance as a coating material required as a coating ground of the cover material of aluminum alloy of the metallic can.
In view of the problem as mentioned above, it is an object of the present invention to provide a non-chromium metal surface treating agent which has excellent adhesion with a coating and corrosion resistance, and also has excellent workability and stability.
The present invention is a metal surface treating agent comprising
a water-soluble zirconium compound, a water-soluble or water-dispersant acrylic resin and a water-soluble or water-dispersant thermosetting crosslinking agent,
wherein said water-soluble zirconium compound has a zirconium content of 500 to 15000 ppm on a mass basis,
said acrylic resin has an acid value of solid matter of 150 to 740 mgKOH/g, a hydroxyl value of solid matter of 24 to 240 mgKOH/g, and a solid matter content of 500 to 30000 ppm on a mass basis, and
said thermosetting crosslinking agent has a solid matter content of 125 to 7500 ppm on a mass basis.
Preferably, the above-mentioned water-soluble or water-dispersant thermosetting crosslinking agent is a condensation product of melamine, formaldehyde and alkyl monoalcohol having 1 to 4 carbon atoms and/or a condensation product of carbolic acid and formaldehyde.
Preferably, the above-mentioned metal surface treating agent treats an aluminum or aluminum alloy so as to provide the water-soluble zirconium compound with zirconium of 0.8 to 35 mg/M2, the water-soluble or water-dispersant acrylic resin with the solid matter of 1 to 60 mg/M2 and the water-soluble or water-dispersant thermosetting crosslinking agent with the solid matter of 0.25 to 15 mg/m2, respectively by mass per one surface after drying.
Preferably, the above mentioned metal surface treating agent treats an aluminum or aluminum alloy.
The present invention is further an aluminum or aluminum alloy, wherein at least one surface thereof is treated with the above-mentioned metal surface treating agent.
Preferably, the above-mentioned aluminum or aluminum alloy is used for a cover material of a beverage can or a food can and further more preferably, it is subjected to a cleaning with acid followed by a treatment with the metal surface treating agent or subjected to a cleaning with alkaline and a cleaning with acid followed by a treatment with the metal surface treating agent.
The present invention is further an aluminum or aluminum alloy
wherein a coat is formed on at least one surface thereof,
said coat containing the water-soluble zirconium compound with zirconium of 0.8 to 35 mg/m2, the water-soluble or water-dispersant acrylic resin with the solid matter of 1 to 60 mg/m2 and the water-soluble or water-dispersant thermosetting crosslinking agent with the solid matter of 0.25 to 15 mg/M2, respectively by mass per one surface after drying.